If you want to contribute new challenges have a look at the random module
Changing current challenges should be done by increasing the version in the Challenge (named Algorithm in code) after changing the corresponding function. You should use somewhat reasonable steps.
For fix 0.0.- For additions 0.-.0 For behaviour change -.0.0 Other contributions are welcomed too.
Some ideas:
layout styling new ways to show the current challenge wording in the code and user interface make challenges more performant